The present invention relates to a control valve for controlling the displacement of a variable displacement compressor used in a vehicular air conditioner.
A typical refrigerant circuit in a vehicle air conditioner includes a condenser, an expansion valve, which functions as a decompression device, an evaporator and a compressor. The compressor draws refrigerant gas from the evaporator, then, compresses the gas and discharges the compressed gas to the condenser. The evaporator performs heat exchange between the refrigerant in the refrigerant circuit and the air in the passenger compartment. The heat of air at the evaporator is transmitted to the refrigerant flowing through the evaporator in accordance with the thermal load or the cooling load. Therefore, the pressure of refrigerant gas at the outlet of or the downstream portion of the evaporator represents the cooling load.
Variable displacement compressors are widely used in vehicles. Such compressors include a displacement control mechanism that operates to maintain the pressure at the outlet of the evaporator, or the suction pressure, at a predetermined target level (target suction pressure). The displacement control mechanism feedback controls the displacement of the compressor, or the inclination angle of a swash plate, by referring to the suction pressure such that the flow rate of refrigerant in the refrigerant circuit corresponds to the cooling load.
A typical displacement control mechanism includes a displacement control valve, which is called an internally controlled valve. The internally controlled valve detects the suction pressure by means of a pressure sensitive member such as a bellows or a diaphragm. The internally controlled valve moves a valve body by means of displacement of the pressure sensing member to adjust the valve opening degree. Accordingly, the pressure changes in a swash plate chamber (a crank chamber), which changes the inclination of the swash plate.
However, an internally controlled valve that has a simple structure and a single target suction pressure cannot respond to subtle changes in air conditioning demands. Therefore, control valves having a target suction pressure that can be changed by external electric current are also used. A typical electrically controlled control valve includes an electromagnetic actuator, which generates an electrically controlled force. The actuator changes the force acting on the pressure sensing member, thereby changing the target suction pressure.
In a displacement control procedure in which the suction pressure is used as a reference, changing of the target suction pressure by electrical control does not always quickly change the actual suction pressure to the target suction pressure. This is because whether the actual suction pressure quickly seeks a target suction pressure when the target suction pressure is changed greatly depends on the magnitude of the cooling load at the evaporator. Therefore, even if the target suction pressure is finely and continuously controlled by controlling the current to the control valve, changes in the compressor displacement are likely to be too slow or too sudden.
Accordingly, it is an objective of the present invention to provide a control valve of a variable displacement compressor that accurately controls the displacement of a compressor and improves the response of displacement control.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a control valve is provided. The control valve is used for a variable displacement compressor installed in a refrigerant circuit of an air conditioner. The compressor has a control chamber and a control passage, which connects the control chamber to a pressure zone in which the pressure is different from the pressure of the control chamber. The displacement of the compressor is varied in accordance with the pressure of the control chamber. The control valve comprises a valve housing, a valve chamber, a valve body, a pressure sensing member, an actuator, and an urging member. The valve chamber is defined in the valve housing to form a part of the control passage. The valve body is accommodated in the valve chamber for adjusting the opening size of the control passage. The pressure sensing member moves in accordance with the pressure difference between two pressure monitoring points located in the refrigerant circuit. The pressure sensing member moves the valve body such that the displacement of the compressor is varied to counter changes of the pressure difference. The actuator applies force to the valve body in accordance with external commands. The force applied by the actuator corresponds to a target value of the pressure difference. The pressure sensing member moves the valve body such that the pressure difference seeks the target value. The urging member is accommodated in the valve chamber. The urging member urges the valve body in a direction to open the control passage.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.